Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantos calibres requerem o tipo LB/RN?
 ###Tabelas: CREATE TABLE women's_singles (women's_singles_id AUTO_INCREMENT PRIMARY KEY, Sd INT, Rk INT, Player VARCHAR, Points INT, Points defending INT, Points won INT, New points INT, Status VARCHAR) CREATE TABLE incorporated_places_with_a_density_of_over_10000_people_per_square_mile (incorporated_places_with_a_density_of_over_10000_people_per_square_mile_id AUTO_INCREMENT PRIMARY KEY, Rank INT, Incorporated place VARCHAR, Metropolitan area VARCHAR, State VARCHAR, Population (2010 census) INT, Land area (mi 2 ) VARCHAR, Population density (people per mi 2 ) VARCHAR) CREATE TABLE all-time_saint_louis_athletica_statistics (all-time_saint_louis_athletica_statistics_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Nationality VARCHAR, Position VARCHAR, Athletica career VARCHAR, Appearances INT, Starts INT, Minutes INT, Goals INT, Assists INT) CREATE TABLE skilift_system (skilift_system_id AUTO_INCREMENT PRIMARY KEY, Name or route VARCHAR, type VARCHAR, elevation groundstation INT, elevation mountainstation INT, slope length INT, capacity in persons/hour INT, construction year(s) VARCHAR) CREATE TABLE threat_levels (threat_levels_id AUTO_INCREMENT PRIMARY KEY, Class VARCHAR, Weapon VARCHAR, Caliber VARCHAR, Type VARCHAR, Weight (g) VARCHAR, Range (m) VARCHAR, Velocity (m/s) VARCHAR, Impact Energy VARCHAR, Shots INT)  
SELECT COUNT Caliber FROM threat_levels WHERE Type = LB/RN